Metal-clad electric switch gear



Jul 23, 1935.

Av ALLAN METAL CLAD ELECTRIC SWITCH GEAR Filed March 1'7, 1953 14 Sheets-Sheet 1 A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet 3 July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet 4 July 23, 1935. A. ALLAN METAL CLAD ELECTRIC SWITCH GEAR Filed March 1'7, 1933 14 Sheets-Sheet 5 Ill IIIIIIIIIIIl/l/ MIME/v T07 July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1953 14 Sheets-Sheet 6 Juiy 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 1'7, 1933 14 Sheets-Sheet '7 mm J NNM

July 23, 1935. A. ALLAN 2,009,333

METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet 8 July 23, 1935. H A. ALLAN 2,009,333

METAL CLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet 9 (T Q N w 3 Mg]: M%

July 23, 1935. A, ALLAN 2,009,333

METAL GLAD ELECTRIC SWITCH GEAR F iled March 17. 1953 14 Sheets-Sheet'lO July 23, 1935. A. ALLAN 2,009,333

METAL GLAD ELECTRIC SWITCH GEAR- Filed March 17, I955 14 Sheets-Sheet 11 July 23,1935.

A. ALLAN 2,069,333

METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet l2 July 23, 1935. A. ALLAN 2,909,333

METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 14 Sheets-Sheet l3 July 23, 1935.

Filed March 17, 1935 14 Sheets-Sheet 14 Patented July 23, 1935 UNlTED STATES PATENT OFFICE METAL-GLAD ELECTRIC SWITCH GEAR Application March 17,

1933, Serial No. 661,404

In Great Britain March 24, 1932 18 Claims.

This invention relates to metal-clad electric switchgear and has for its primary object to provide an improved arrangement of the metalclad apparatus (such for example as circuitbreakers, reactors and transformers) forming part of or associated with a switchgear layout for an electric power station or substation, whereby considerable economy can be effected both in the size and the cost of the switchgear.

Metal-clad switchgear according to the present invention comprises a chamber containing a busbar or other conductor immersed in an insulating liquid, a movable conductor which in its operative position projects through an orifice in the wall of the chamber and makes contact with the busbar or other conductor therein, and a sealing device so arranged as to seal the orifice in a liquid-tight manner when the conductor is withdrawn from the chamber. The arrangement is especially suitable for the case of a movable conductor connecting two conductors each mounted in a chamber containing insulating liquid, the movable conductor in this case being withdrawable into or through one of the chambers whilst a sealing device is provided to seal the orifice in one or in each of the chambers. Thus one convenient arrangement according to the invention may comprise a tank containing a circuit-break or or other electrical apparatus, a chamber containing a busbar or like conductor immersed in an insulating liquid, an insulated conductor so mounted that it can project into the apparatus tank and the busbar chamber to connect the busbar to a terminal of the apparatus and can be withdrawn from the busbar chamber towards or into the apparatus tank, and a sealing device so arranged as to seal the orifice in the wall of the busbar chamber in a liquid-tight manner when the insulated conductor is withdrawn therefrom into the tank. The orifices in the walls of the two chambers through which the insulated conductor passes are preferably connected together by a metal trunk carried at one end by one of the chambers and provided at the other end with a flexible extension detachably connected to the wall of the other chamber. The detachable con- .ection may take various forms but in one convenient arrangement the flexible extension is mechanically forced, for example, by a toggle mechanism, into close contact with the chamber wall around the orifice so as to seal the joint in a liquid-tight manner.

An alternative rrangement according to the invention comprises a chamber containing a busbar or like conductor immersed in an insulating liquid, a tank containing a circuit-breaker or other electrical apparatus movably mounted with respect to the busbar chamber for isolating purposes, an insulated conductor mounted on the apparatus tank and connected to a terminal of the apparatus therein and arranged that when the apparatus tank is in its operative position the insulated conductor projects through an orifice in the wall of the busbar chamber and makes contact with the conductor therein, and a sealing device so arranged as to seal orifice in the busbar chamber in a liquid-tight manner when the apparatus tank is moved to withdraw the insulated conductor from such chamber.

Except in arrangements, such as that just mentioned, wherein the movable conductor is fixed in position on a movable tank, the movements of the conductor are preferably effected by fluid pressure operated means, for example, by arranging the insulation around the conductor or a metal sheath surrounding such insulation to act as a piston in a tubular sleev The manner in which the sealing device is mounted may vary; In one simple arrangement the device is in the form of a plug detach-ably carried by the movable conductor so that it will remain in and seal the orifice in the chamber wall when the conductor is withdrawn. Alternatively the device nay be in the form of a plug hinged or otherwise mounted on the wall of the chamber to be sealed, means being provide-z for moving the plug into its sealing position when the conductor is withdrawn. In a pre' rred arrangement the sealing device is in the rorm of a sluice valve which is carried on the wall of the chemher to be sealed and can slide to seal the orifice when the conductor is withdrawn.

It will be appreciated that the provision of the sealing device according to the invention ensures that there will always be a body of insulating liquid between the busbar or other conductor and the earthed metal wall of the chamber around the orifice even at the moment when the insulated conductor is being withdrawn from the chamber, and thereby renders it unnecessary to provide the large clearance distance between these points which would otherwise be r quired to prevent risk of a fiashover ii the space between these points were at any time filled with air. This makes it possible considerably to reduce the size of the chamber, and therefore also the cost of the whole installation, since it is only necessary to separate the busbar fro .l the walls of the chamber by a distance sufiicient to prevent risk of a fiashover in oil. Another great advantage of the invention is that it enables the removable portions of the switchgear to be separated from oil-filled chambers in the. stationary part without the necessity of draining the oil out of such chambers and therefore without introducing the dangerous condition of air clearance to a live contact at any time even during actual removal of the circuit-breaker or other apparatus.

The invention may be carried into practice in a variety of ways, but some convenient practical arrangements according thereto, as applied to oil-immersed circuit-breakers forming part for example of a high voltage switchgear layout, are illustrated in the accompanying drawings, in which Figure 1 is an elevation (with the circuitbreaker tank in section) of anarrangement in which the circuit-breaker controls a simple'connection from a busbar to a feeder or other circuit,

FigureZ is an enlarged sectional View of part of Figure 1 showing thearrangement'of the withdra'wable conductor,

Figures 3 and 4 are vertical and horizontal sectio'ns through the sealing device,

Figures-5 and Gare detached views on a larger scale of parts of Figure2,

Figure '7 illustrates'a modification of the arrangement'of Figures-l-S for the case of a duplicate busbar installation,

Figures-8 9 'areviews similar to that of Figure '7 showing alternative constructions of withdrawable conductor,

Figure 10' illustrates an alternative duplicate busbar arrangement,

Figure 11 is a side elevation of a low-voltage three-phase switchgear arrangement,

Figure l2 is a front elevation (with the sup porting 'framework removed) of the arrangement of Figure ll, parts being shownin section,

Figure's l3 and 14 are respectively aside elevation and a front elevation of an alternative lowvoltage arrangement,

Figure 15 is 'asectional view of part of the arrangement of Figures '13 and '14, V

Figure 16 is a view similar to that of Figure 15 showing 'a modified arrangement,

Figures 17 and 18 are sectional views respective'ly illustrating-two alternative forms of sealing device,

Figure '19 illustrates a further alternative form of sealing device, 7 r V Figure "20 is a section on the line 20 23 of part of-the arrangement of Figure 19,

Figure 21 illustrates the application of the inventionto switchgear of the horizontal drawout type,

Figure 22 illustrates an alternative driving arrangement for the withdrawable conductor,

Figure 23 illustrates a further alternative duplicate busbar arrangement, and

Figures 24 and "25 respectively illustrate mod-ifications of the arrangement ofFigure 23.

In the arrangement shown in- Figures 1-6, which is applicable to a simple installation in which the circuit-breaker controls a "connection from a busb'ar to Ja-"fee'cler or other circuit, the circuit-breaker oil tank 53 rests on the ground "and two oil-filled chambers 6 3 and "it 'aremounted above the tank on supporting pillars or a'suitable framework (not shown). The chamber '60 constitutes the busbar chamber and contains a contact 6! to which the sections of the'busbar "62 are directly connected. 7

The chamber T6 is associated withthe feeder circuit and contains a contact "H carried by 'a 'to the chamber wall around the orifice with suitable insulation to isolate the cable sheath from the chamber wall. A small compartment is thus enclosed between the sealing end ii! and the hollow insulator i3 and this compartment may be filled with oil from the chamber '1' th ough a valve on the insulator l3. Means are provided to allow the oil to be drained oif from this compartmentafter closing the valve, when it is desired to remove the sealing end, and it will be I appreciated that this arrangement permits removal of the sealingend without the necessity for draining the oil :out from the chamber it itself.

The circuit breaker comprises two fixed main contacts El, 52 and-a movable bridging contact member 53, the arrangement preferably being such as to give six breaks in series. The bridging contact member 5% is operated by suitable mechanism, indicated-at ca plate E5 of the oil tank containing the circuit-breaker.

Extending upwardly at a small angle to the vertical from each of the 'fixed-main 'contacts iii, 52 of the circuit-area er'ishollow condenser insulator 8t, comprising shortoverlapping conducting layers 8iinte'rleave-d with insulating layers and surrounded inits upperpor'tion by a metal sleeve82, which projects'threu'gh an orifice in the cover plate 55 of the tank and is provided with a flange 83 bolted to thecover plate; The lower end ofeach hollow insulator-8e is closed in an oil-"tight manner by a'metal cap 3 connec'ted to themain'iixe'd circuit-breaker contact 5! "or eland a met'al tube extends up from this cap 3 \vithin'th e lower portion or". the insulator. At the upper end of each insulator the surrounding metal sleeve' e'2 carries a flange to which is bolted a metal casing including a cylindrical metaltrunkfil surrounded by an annular chamber 32 in which current'transformers can be located. Around'the upper end of the metal trunk i a flexible metal bellows which'is attached to th-etop'of the casing and can beclamp'ed to the bottom of a valve chest mounted belowth appropriate oil-filled chamber or 'iii, a metal shieldiifi being provided around the bellows 93 to protect it from dama e. busbar 'contac't E-i or the 'ieedercontaot'? i, as the "c'ase'may be, is in line with the axes of'the metal trunk 9i and the hollow insulator 3t, and com munication between the chamber SE was a-nd the tubular compartment formedby the'trun-k and the insulator can be cut on by means of a valve in the valvechest in a manner to be describes later. 1

Mounted to slide longitudinally in this tubular compartment is an insulated conductor it, which serves when in its operative position to connect the busbar Contact 'Si or the feeder contact H to the inner metal "tube 35 in the insu lator 80 and thence to the circuit-breaker contact fii or 52. This insulated "conductor 'ccn prises a rigid central tubeiti surrounded by insulation Hi2, which in the case of the higher rried by the cover 5 voltage installations is in the form of condenser insulation as shown, the insulation being enclosed for part of its length by an outer metallic sheath Hi3, which engages with the metal trunk 9 i. The central tube IGi serves to contain flexible connections I34 between contacts at the upper and lower ends of the insulated conductor. The lower contacts (see Figure 6) are in the form of outwardly spring-pressed plungers I05 engaging with. the metal tube and carried in a metal block IE8 to which the lower ends of the flexible leads I534 are connected. The upper contacts consist of a bundle of butt contacts l0! independently spring-pressed in a longitudinal direction so as together to constitute a self-aligning butt contact for engagement with the busbar contact GI or the feeder contact II.

The insulated conductor can be withdrawn downwards from its operating position into an isolatmg position, in which it lies within the tubular compartment formed by the metal trunk S! and the insulator 88. In Figure l the conductor associated with the feeder is indicated in its ra' ed ope-rating position, whilst that associated the busbar is shown withdrawn into its isolating position, and Figure 2 similarly shows the conductor in the isolating position.

The movements of the withdrawable conductor are effected hydraulically by varying the oil pressure above and below the conductor, the metal sheath I03 on the conductor being provided with piston rings I 08 so that the sheath acts as a piston movable in a cylinder constituted by the metal trunk 9!. For this purpose an oil pump HG driven by an electric motor iii is mounted on the casing and is connected by suitable ducts ME, I I 3 to the upper and lower ends of the tubular compartment in which the with drawable conductor moves. The upper duct H2 opens into the transformer chamber 92 and is thus connected through the interior of the metal bellows 93 to the open upper end of the metal trunk 9|. The lower duct H3 opens into the lower part of the casing beneath the transformer chamber and is thus connected through openings in the flange 88 to the interior of the insulator 86, parts of the metal sheath I93 being cutaway as indicated at 39 to permit the oil to flow into the lower end of the insulator 80. Thus to raise the conductor the pump H0 is started up to withdraw oil from the upper end of the trunk 9i and to drive it into the interior of the insulator Bil. To lower the conductor the pump is driven in the reverse direction, the weight of the conductor assisting the movement. Alternatively a by-pass valve may be provided, which is opened to connect the two oil ducts together, the weight of the conductor being relied upon to effect the downward movement. If desired, instead of forming the sheath I33 as a piston moving in the cylinder formed by the metal trunk 9i, the upper and lower parts of the tubular compartment may be separated from one another by a cup leather or sealing ring fixed in the metal trunk and embracing the insulated conductor, so that the movements of the conductor are effected after the manner of a hydraulic ram.

Whilst the oil pressure may be utilized to hold the insulated conductor in its raised operating position, it will usually be preferable to provide a mechanical latch for this purpose. A convenient construction of latch, which will hold the conductor either in its operating position or in its isolating position, is shown in Figures 2 and 5. This latch consists of a ring I20 surrounding the insulated conductor and pivoted about a vertical pin I2I at the lower end of the casing St] at one side, the ring having two internal flanges 522 and I23 at different levels on opposite sides of the conductor. These flanges cooperate with grooves I24 and I25 in appropriate positions in the metal sheath I03 of the conductor, and to ensure correct positioning of the lower groove I25 a collar 95 is provided at the upper end of the metal trunk 9| with which the upper end of the metal sheath I03 engages when the conductor is in its raised position. The metal block 13% containing the lower contacts 35 similarly engages with a shoulder 85 at the lower end of the metal tube 85 within the insulator 80 for positioning the upper groove I24 correctly when the conductor is in the isolating position. The latch ring 128 is moved one side or the other about its pivot I2I by a pair of spring crank arms I39 on a horizontal shaft I31 suitably mounted outside the metal sleeve 82. The shaft I3! is rotated by an operating arm I32 movable between fixed stops I33, I34 under the control of an operating rod I35 (see Figures 1 and 2). Thus with the conductor held in its raised position (as indicated on the right-hand side of Fig. 1) by the engagement of the lower latch flange I23 in the lower groove E25, movement of the operating arm i3? to its other limiting position against the stop 63:1 will cause the spring arms I33 to release the flange 23 from the groove I25 and will hold the upper latch flange I22 spring-pressed against the surface of. the metal sheath I33, s that when the conductor reach s its isolatirn position (as indicated on the left-hand side of Figure l) the upper latch flange I22 will spring into engagement in the upper groove I24, the converse latch operation taking place when the conductor is raised. The latch operating mechanism is also utilized to operate through levers I35 a number of auxiliary switches in l housed in a box 938 on the casing 99 for indicating or interlocking purposes. The shaft of the auxiliary switches may also operate an indicator visible through a window I39 on the box I38 to indicate wh conductor is in its operating position or in its isolating position. The latch-operating rods 535 are actuated by suitable control mechanic- 1 which also operates contacts controlling the energisaticn of the electric motors III for driving the pumps, the energizing circuits for the pump niotors being taken through certain of the auxiliary switches I3? controlled by the latch, the arrange ment being such that a pump motor cannot be energized until the corresponding latch has been released.

As has been mentioned, a valve is provided for sealing the orifice at the bottom of the busbar chamber 65 or the feeder chamber '58 when the insulated conductor has been withdrawn. A preferred construction for this valve is indicated in Figures 1 and 2 and is shown in detail in Figures 3 and 4. In this arrangement the valve is mounted in a valve chest M9 and is in the form of a sluice valve MI, which is caused to slide over the orifice by r tation of a screwthreadcd shaft M2 by means of a handwheel M3. The valve shaft Hi2 carries a notched disc I44, with which an arm M5 carried by a spindle I46 cooperates. This spindle I45 is connected to part of the control mechanism for actuating the associated latchoperating rod K55, the arrangement being such that when the control. mechanism is operated to cause the insulated conductor to be raised, the spindle I46 is rotated to cause the arm I45 to air into the upper chamber.

engage in a .notch on .the disc M4 and thus to prevent the handwheel I43 from being rotated to close the valve. Since the arm 1% *maynot always be opposite a notchin the disc Hi l, the spindle M6 is made of sufiicient flexibility to permit it to twist when operated, so that after a slight rotation of the handwheel, the arm M5 will spring into the first notch on the disc and willthus lock the handwheel against further rotation. In order to prevent energization of the pump motor iii to raise the insulated conductor when the sluice valve is closed,the energizing circuit to the pump motor is controlled by an auxiliary switch operated by the sluice valve. For this purpose the valve shaft M2 carries a worm M? for operating a rotary .auxi-liary switch M8 housed. in a casing M9 carried by the valve chest.

At one side of the valve chest MD, a by-pass valve is provided in the form of a rotary tapered plug E59 having two holes 15!, E52 bored in it. One of thcse'holes lt-I cooperates with two passages (one of which is indicated at 553) in the valve chest communicating respectively with the spaces above and below-the valve itself. The second hole l52 controls a connection from the space below the valve to the atmosphere. In the normal position of the plug l 55 both holes are closed, but by rotating the plug into one position it is possible to complete a by-pass connection through the-hole i5! from one side of the valve to the other and at the same time a further connection from the space below the valve to the atmosphere. This allows the interior of the bellows 93 to be filled with oil from the upper chamher, when the bellows is again connected thereto after having been disconnected for removal of the circuit-breaker, without permitting entry of The plug l 59 can also be rotated into a further position in which the by-pass connection is closed, but the connection of the space below the valve to the atmosphere through the hole G52 is open. This position is utilized to permit air to enter the interior of the bellows 93, when oil is being drained therefrom by a suitable draincock (not shown) prior to disconnection of the bellows from the upper chamber. In the body of the sluice valve I l! it elf two small non-return valves E55, I56 are provided which act in opposite directions. The valve l55is arranged to open when the pressure in the upper chamber exceeds that within the bellows by a predetermined amount to permit oil to flow into the bellows when contraction of the oil below the valve takes place as the result of temperature variations, and the valve I56 likewise allows oil to flow out from the bellows into the upper chamber in the event of excessive pressure being set up within the bellows owing to expansion'of the oil therein due to temperature changes. I

.The above arrangement may be modified in various ways. Thus for instance the hollow insulator Bil in the circuit-breaker tank may be taken The foregoing arrangement has been described and illustrated as applied to a circuit-breaker controlling a simple connection from a busbar to a feeder circuit, but it is equally applicable to the case of a duplicate busbar layout wherein each busbar is connected to the feeder or other circuit through a separate circuit-breaker, and generally to all cases where it is impossible for the fixed circuit-breaker contact with which the insulated conductor'cooperates to be alivefrom another circuit during movement of the insulated conductor from one position to the other. Thus in the arrangement actually illustrated in Figures 1-6 the metal sheath 593 of the conductor connects the circuit-breaker contact through the tube to the earthed metal trunks and even if the metal sheath were shortened to'avoid such a direct earth connection, the inclusion of metal layers in the insulation around the conductor would in many instances reduce the dielectric value of the insulationv between the circuit-breaker contact and the earthed metal trunk totoo low a value. In cases therefore where the circuit-breaker contact may be alive from another circuit and where it is desirable to employ condenser insulation around the conductor, it is preferable to modify the construction of the insulated conductor to avoid risk of flash-over from the main circuitbreaker contact to earth.

Figure 7 illustrat s such a modified form of insulated conductor in its application to a duplicate bushbar installation, wherein a single circuit-breaker provided with busbar selecting means controls the connections from bothbusbars to the feeder or other circuit. In this arrangement three oil-filled chambers are mounted above the circuit-breaker oil tank, two of these chambers respectively containing contacts connected to the two busbars, whilst the third contains a contact connected to the feeder or other circuit. The three contacts in the upper-chainbers are connected to the circuit-breaker fixed contacts by withdrawable insulated conductors, the conductors associated with the two busbar contacts both cooperating with one of the main circuit-breaker contacts, whilst the other main circuit-breaker contact cooperates with the con ductor associated with the feedercontact.

Figure 7 shows the two busbar chambers 5'38 and H5 respectively containing contacts ill and H6 connected to the two busbars 572 and ill, and the connections therefrom to one of the fixed main circuit breaker contacts l8 5 contained within the circuit-breaker tank 585]. The other circuit-breaker contact and the connection therefrom to the contact in the feeder chamber are not shown in the drawings but are preferably identical .with the corresponding parts of the arrangement of- Figures 1-6, and a description of the connections to the busbars will be sufficient to enable the'whole arrangement to be understood.

Mounted one on either side of the circuitbreaker'contact l8! are two hollow insulators I90, each surrounded at its upper portion by a metal sleeve E carrying a. flange H2 bolted to the cover plate 532 of the tank. Each insulator extends down past the circuit-breaker contact i8! and a connection from this contact passes through the wall of the insulator to an internal ring contact 593. The insulator is closed at its lower end by a metal cap i9 3, carrying a short internal tube 35, and to grade the stresses set up the insulation is in the form of condenser insulation with suitably arranged overlapping short metal layers I96 interleaved with the insulating layers. The flange I92 at the upper end of the metal sleeve I9I carries a metal tube I91 extending from within the top of the insulator I90 upwardly and having at its upper end a flange I68. to which is bolted a casing 206 containing a cylindrical metal trunk 26I surrounded by 21. current transformer chamber 292, the metaltrunk constituting a continuation of the metal tube I 91. The casing 260 and the parts carried thereby (including the motor-driven pump and the latch device) are substantially identical with the corresponding parts of the arrangement of Figures 145. A valve chest 205 containing a sluice valve is mounted beneath the busbar chamber as in the previous arrangement and is similarly connected to the top of the casing 20!! by a flexible metal bellows 205.

Mounted to slide longitudinally in the tubular compartment constituted by the metal trunk 20 I, the metal tube I9! and the hollow insulator ISO, is an insulated conductor, which serves when in its operative position to connect the busbar contact ill or Ilt to the ring contact I93 and thus to the main circuit-breaker contact I8I. This insulated conductor comprises a rigid central tube 2H3 containing flexible leads connecting upper butt contacts 2H and lower spring contacts M2 in a manner similar to that described with ref erence to Figures l-6. The central tube 2H3 is surrounded by layers of paper insulation 2 IS interleavedwith overlapping short metal layers 2I=I and the upper part of the condenser insulation is enclosed within a metal sheath 2l5. Spring contacts 2I6 are provided on one of the intermediate metal layers approximately midway between the lower end of the conductor and the lower end of the sheath 2I5. The metal sheath 2I5 carries piston rings 2II sliding in the cylindrical metal trunk 2M and is provided with upper and lower grooves 2MB, 2 I9 coacting with the latch device in the casing 200 in a. manner similar to that described for the arrangement of Figs. 1-6.

Since the metal sheath 2I5 slides within the metal trunk 21H it always remains in contact with earthed metal. When the insulated conductor is in its operative position with its upper butt contacts 2 II engaging with the busbar contact and its lower spring contacts 2I2 engaging with the ring contact E93 connected to the circult-breaker contact the contacts 2I5 on the intermediate metal layer are earthed through the metal tube I 9'! (as indicated on the right-hand side of the drawings), whilst when the insulated conductor is in its isolating position (as shown on the left-hand side) the intermediate contact 2IB engages with the ring contact I93 and the central conductors are earthed through the short tube 195 on the bottom cap I84 on the hollow insulator I90. Thus in the isolating position the intermediate contact 2I6 may be alive, owing to the connection of the circuit-breaker contact I8! to the other busbar, but is located between two earthed points from which it is separated by condenser insulation.

Thus with the circuit-breaker in operation connesting the feeder to, say, the busbar I", the insulated conductors associated with the feeder and with this bushar will both be in. their raised opera tive positions, whilst the insulated conductor associated with the busbar I12 is in its isolating position. If now it is desired to change over to the busbar 12, the main circuit-breaker contacts are openedv and the insulated conductor for the busbar Ill is lowered by operation of its pump and latch device, the insulated conductor for the busbar I12 then being raised into its operative position and the main circuit-breaker contacts closed. The change-over can alternatively be eilected without opening the main circuit-breaker contacts by first raising the insulated conductor for the busbar I72, so that the two busbars are connected together and to the feeder, and then lowering the conductor for the busbar ill. To remove the circuit-breaker for inspection or over .111, the procedure is similar to that for the arrangement of Figures 1-6, namely, to open the circuit-breaker contacts and lower all the insulated conductors, after which the sluice valves are closed and the flexible bellows detached (after draining the surplus oil out of them). The circuit-breaker operating mechanism, if it is not arranged to be movable with the circuit-breaker, is then uncoupled, so that the circuit-breaker with the insulated conductors inside it can be removed laterally without the necessity of lowering it.

Instead of employing two separate tubes I9? and Bill in line with one another, the cylindrical metal trunk 2M may itself be extended downwardly to beyond the cover plate I82 of the tank, the metal sleeve I9! and the hollow insulator I99 then extending right up to the flange I98 with the metal trunk 28! within the insulator. This modification is shown in Figure 8, which also shows a modified arrangement or" the insulated conductor. In other respects the arrangement of Figure 8 is similar to that of Figure '7 and the same reference letters are employed. The insulated conductor employed in the arrangement of Figure 8 has a central tube 2IO with the internal leads connecting the upper and lower contacts 2! i, 2 l 2 and also a metal sheath 2I8 with its piston rings 2H and grooves 2I8, 2I9, as in the arrangement of Figure 7, but it differs from that arrangement in the form of the condenser insulation. In the arrangement of Figure 7 the overlapping short metal layers 2 I4 in the lower part of the insulation extend from close to the central tube 248 the lower end of the conductor at steadily increasing radii right up to the lower end of the metal sheath 2I5, the spring contacts ZIE being connected to a layer at an intermediate radius. In the arrangement of Figure 8, however, overlapping short metal layers 220 extend from close to the central tube 2H1 at the lower end of the conductor to a layer 22I at the full radius of the metal sheath 2I5 but at a position in the length of the conductor corresponding to that of the spring contacts 2 I 6 in the arrangement of Figure '7. This layer22l is connected through the insulation to spring contacts 222. A further series of overlapping short metal layers 223 extends from close to the central tube are directly within the layer 22I up to the lower end of the metal sheath M5. At the upper end of the conductor, both in this arrangement and in the arrangement of Figure '7, a similar series of overlapping short layers is provided between the sheath 2 I5 and the upper end of the conductor, and the layers at the upper end are separated from the layers at corresponding radii in the lower part of the conductor by a considerable axial distance which is such as to ensure adequate insulation between the circuitbreaker contact and the earthed metal trunk at all stages in the movement of the insulated conductor.

In the arrangements shown in Figures -8 the insulation around the withdrawable conductor has in each case been described as of the graded condenser type. Whilst this is generally preferable in the case of apparatus used in high vol age in tallations on account of the reduction in dimensions which it allows, it may in some instances be more advantageous to employ an'oil filled type of insulating bushing around the o ductor. Such an arrangement i shown in Figur- 9 for a duplicate busbar installation.

With the exception of the insulated conductor itself, this arrangement is identical with that shown in Figure '7 and the same reference letters are employed. 7 The withdrawable insulated conductor shown in Figure 9 comprises a rigid central tube which may itself constitute the conductor or enclose flexible leads in the manner above described, an upper butt contact 23!. and lower spring contacts 232 being provided. A number of concentric insulating tubes 233 of graded lengths surround the central tube 23H within an outer insulating sleeve 23. the intervening spaces being filled with oil, so that the conductor is surrounded by a series of more or less uniformly thick layers of oil alternating with solid insulating layers. The outer sleeve withdrawable conductor is utilized for controlling the connections from one circuit-breaker contact to the two busbar contacts, whilst the other circult-breaker contact is connected to the feeder contact by a withdrawable conductor, which is arranged (together with the parts within which it moves) exactly in the manner shown in Figures 1-6. Figure 10 illustrates only the parts of the arrangement associated with the busbar side of the circuit-breaker;

In the arrangement of Figure 10, the two busbar chambers 25c, Edi are mounted close together above the circuit-breaker tank, and each is pro vided beneath an orifice in its bottom wall with a valve chest 255 containing a sluice valve arranged in the manner previously described. The fixed circuit-breaker contact associated with memo busbars is supported beneath a hollow insulator 268 of oval cross-section carried by the cover plate 265 of the circuit-breaker oil'tank, and is connected through the bottom of the insulator to a curved "contact member Efil. Extending up from the cover plate 2555 towards the twobusbar chambers is'a metal casing 278 of generally oval cross-section, to the upper end of which is attached a flexible metal bellows 2W which can be clamped to a suitable oval fitting 2% carried beneath the two valve chests 255. This casing carries a hollow horizontal shaft 2l2 about which is pivoted an inner metal casing 289 carrying at its upper end a cylindrical metal tube 285 and at its lower enda metal sheath 282 for a condenser insulator 283. This insulator is closed at its lower end by a metal cap 285 having a projection ZSS'engaging with'the curved contact member carries a metal sheath providedwith piston rings 235. and upper and lower latch aooass's permanently connected to the fixed circuitbreaker contact. The metal tubes 2st and 285 are in line with one another and the metal casing 288 can be swung about the shaft 2'12 by suitable means (not shown) between two positions in which the axis of the tubular structure EBLZBB is in line respectively with the busbar contacts in the two busbar 'chambers'Zfill and 255. An insulated conductor 296 generally similar in construction to those employed in the arrangement of Figures l dhas its metal sheath 29:? provided with piston rings292 sliding within the metal tube 28!, so that its lower spring contacts 2% always engage with the metal tube whilst its upper butt contacts 2% can engage with either busbar contact. The metal sheath 2% has upperand lower grooves 295, 2st cooperating with a latch device 29? operated by a latch-operating rod 293 outside the casing are through a universal coupling 299. The conductor is raised and lowered hydraulically within the surrounding tubular. structure by meansof a motor-driven pump 2E3 carried by the casing 278, on side of the-pump communicating directly with the interior of the casing 21 8 through a duct 2%, whilst the other side communicates with the interior of the pivoted inner casing 283 through a pipe 275 coupled to the hollow shaft 272. Thus to change over from one busbar to another the circuit-breaker contacts are first opened and the insulated conductor is withdrawn into the tubular structure 28L 2%, after which the inner casing 28 is rocked about its pivot to the other position and the conductor is raised again into engagement with the other busbar, the circuit-breaker contacts then being reclosed. The circuit-breaker can be removed for inspection or repair, when the insulated conductor has been withdrawn by detaching the flexible bellows fall from the busbar chambers.

Figures 11 and 12 illustrate the application of the invention to a relatively low voltage threephase switch-gear installation. In this arrangementthree single-phase circuit-breakers 353 are mounted one behind the other on a wheeled truck Bel. Each circuit breaker has two fixed main contacts 3% cooperating with a movable main contact 393 and four sets of arcing contacts 3% are provided with one set on eachside of each fixed main contact. Extending vertically up- Wards from each circuit-breaker fixed main contact 3&2 is a tubular structure containing a with drawable conductor, the six tubular structures being in line with one another. Each tubular structure comprisesa hollow insulator 358 surrounded in its upper part by a metal sheath 3H and closed at its lower end by a metal cap 352 which is connected to the fixed circuit-breaker contact Strand carries a metal tube Bit extending up within the insulator 35 3. The metal sheath Si! is flanged for attachment to an upward projection 366 on the cover plate 335 of the circuit-breaker tank and carries an upper casing 35 within which is mounted a cylindrical metal trunk 3P5. Attached to the top of the casing 316 is a flexible metal bellows tit, which can be clamped to the under side of a valve chest 328 containing a sluice valve arranged in the manner above described. The six valve chests 32B are respectively secured beneath six upper oil-filled chambers carried on a suitable supporting framework 32!, three of these upper chambers constituting busbar chambers 32-2, whilst the other three are feeder chambers 323. Each of the busbar ch'ambers 322 has in it a contact 324-, having a downwardly extending cylindrical flange 

